Bat Detector: Listen to the Secret Sounds of Bats
Abstract Do you have bats in your neighborhood? Have you heard them "whoosh" by you, but not been able to see them? In this science fair project, you will be able to detect flying bats by listening in on the ultrasonic signals they produce to locate objects in their environment. The bat detector is a useful and fun tool for studying the biology of this nocturnal flying mammal. Objective The objective of this mammalian biology science fair project is to study the behavior of bats in the wild, based on the sounds they make. You will use a device that is designed to detect the ultrasonic pulses made by bats. Materials and Equipment *Purchase a frequency division bat detector. Two online sources are Edmund Scientific catalog # 3085040 and Convergence Tech, Inc. *A digital recording device to record bat sounds; a laptop with a microphone will also work *Optional: use a video recorder to document your observation sessions. *Lab notebook *Graph paper Introduction Bats are the only mammals that have wings and the ability to fly. Their wings are made of a membrane, the patagium, that is an extension of the skin from the back and belly area. Their wingspans vary from 5 feet in the large flying fox bat to 6 inches in the hog-nosed bat. Table 1. This table shows the classification for bat species. Bats belong in the order Chiroptera. Chiroptera is a huge order, containing nearly one-quarter of all mammal species. It is exceeded only by rodents in the number of species that comprise it. Bats are divided into two sub-orders, the Megachiroptera and the Microchiroptera. Megachiroptera tend to be bigger than the Microchiroptera, have a fox-like face, and lack features for echolocation, which is a way of locating distant or invisible objects, like prey, by sound waves that are reflected back to the emitter, such as a bat, from the objects. All Microchiroptera, on the other hand, use echolocation to find prey and to navigate while flying at night. Echolocation calls are vocalizations that are produced in the larynx (voice box) and then sent out through the mouth or the nostrils. Like other types of sound, bat signals are transmitted through the air as vibrations, or periodic fluctuations in air pressure. The pitch of the sound is determined by its frequency. Frequency is measured in hertz (Hz), or cycles per second. The unit'kilohertz (kHz)' is equal to 1000 Hz. Echolocating bats emit an ultrasonic pulse and analyze the returning echo to determine the distance to the object, its speed, as well as what type of object it is. Ultrasonic signals, by definition, have frequencies that are higher than the upper limit for human hearing, which is about 20 kHz. Most bats alternate between emitting sound and listening for returning sound. Bats can change the design of their calls to fit the task—navigating, searching for flying insects, or snatching insects off of plants. The ability to echolocate has allowed many bats to exploit flying nocturnal insects as a food source, as well as to live in dark caves. Most likely as a result of increased reliance on echolocation, microchiropteran bats have reduced vision capabilities, having lost some of the complexity found in the eyes and brains of megachiropteran bats, but it not true that bats are blind! Interestingly, some moths have evolved the ability to hear the echolocating sounds made by bats. When one of these moths hears calls of an approaching bat, it might make evasive maneuvers. Some insects actually emit sounds in response to bat calls. This apparently confuses the bat, although it does not directly jam the signal. Because the frequencies of bat sounds are too high for humans to hear, scientists use bat detectors to transpose bat sounds to a lower frequency. For this science fair project, you will use a frequency division bat detector. These instruments lower the pitch (frequency) by a factor of 16 so the calls fall within the range of human hearing, which is between 20 and 20,000 Hz. For example, a call that was originally 64,000 Hz is played back at 4,000 Hz (4 kHz) with the frequency division bat detector. You can hear an example of a recording made using this type of bat detector at the USGS link in the Bibliography, below. There are other types of detectors besides the frequency division type, but they tend to be more expensive. Before you start this science fair project, you should have a good idea of where you will go to study bats in your area. They are active starting a few minutes after sundown, which is a good time to go because you might be able to see them in the dim light. Wooded areas and freshwater sources are good places to spot them. Do your research before you start so that you can predict what species of bats you are most likely to encounter. Take an adult with you to help, and don't forget your bug spray! Terms and Concepts *Patagium *Chiroptera *Megachiroptera *Microchiroptera *Echolocation *Frequency *Hertz (Hz) *Kilohertz (kHz) *Ultrasonic *Frequency division bat detector *Qualitative *Quantitative Questions: *How do bats use echolocation to navigate and find prey? *Do any other animals use echolocation? *What do bats do during the winter when there are no insects to eat? *What positive contributions do bats make to our environment? (Hint: what diseases can be transmitted by mosquitoes?) *Are bats rodents? *What do the bats eat? Photos Category:Mammalian Biology Experiments